This invention relates to a device for automatically recognizing two-dimensional input patterns which may be handwritten letters, numerals, and accompanying marks.
Character recognition devices have been much in demand as input devices for putting data and programs into electronic computers and those for automatically recognizing printed character patterns are already widely used. It is to be noted here that most of the data and programs for computers must be once written on paper by hand and that there accordingly is an eager demand for devices for automatically recognizing these handwritten character patterns. Handwritten character patterns, however, widely vary. No techniques have therefore been known for satisfactorily recognizing the handwritten character patterns. This has made it inevitable at present to impose a severe restriction upon the style of the handwritten character patterns in order to meet the requirements for automatic recognition thereof. Devices for recognizing handwritten character patterns with such a restriction are in practical use despite the fact that the restriction is inconvenient and undesirable for those who actually write the characters.
In general, a character recognition device comprises an input unit for converting the optical signals produced by two-dimensional input patterns into electric signals and a recognition unit for carrying out logic or arithmetic operation on the electric signals to decide the input patterns. Inasmuch as input units of excellent performance are already available, it is the recognition unit that poses a serious problem to be solved on designing a device for automatically recognizing handwritten character patterns. Among various principles on which the recognition units are operable, the pattern matching method is simple and most frequently resorted to. According to the pattern matching method described in detail by M. B. Clowes and J. R. Parks in The Computer Journal, Volume 4, No. 2 (1961) pp. 121-128, the input character patterns are subjected to comparion or pattern matching with standard or reference character patterns (hereafter called "standard patterns" for brevity) preliminarily prepared for all sorts of the character patterns to be recognized and are decided to be those of the standard patterns which are in best coincidence or agreement with the respective input character patterns. Although effective for recognition of input character patterns of a predetermined type, such as printed ones of several predetermined fonts or those handwritten under a severe restriction, this method is liable to mis-recognition in the case of character patterns handwritten without much care because even a slight departure or deviation from the standard patterns renders the agreement therewith unstable. In the nearest neighbor method described in IEEE Transactions on Information Theory, Volume IT-13, No. 1 (January, 1967), pp. 21-27, the abovementioned pattern matching method is adapted to recognition of character patterns liable to deviation to a certain degree. In accordance with the nearest neighbor method, a plurality of standard patterns of different styles are prepared instead of only one used in the pattern matching method for each sort of the character patterns to be recognized. It is, however, necessary for a device according to the nearest neighbor scheme to memorize a great number of standard patterns and to carry out the comparison a corresponding number of times. The device therefore becomes complicated and expensive if designed for automatic recognition of character patterns manually freely written.